1. Field of the Invention
The present invention relates in general to the field of security devices, and, in particular, to a system which may be utilized to track the whereabouts and status of a plurality tracking units carried by persons or items located about a substantial area of interest such as an office building, school campus, hospital, or prison facility, and to communicate data on the status of these persons or items to a central monitoring station.
2. Description of the Prior Art
There has long been a need for a security system to provide accurate, meaningful, real time monitoring of persons and objects throughout large areas such as automobile sales lots, office buildings, school campuses, hospitals, and prison facilities. In order for security and loss-prevention professionals to adequately protect the persons and property under their care and supervision, it is necessary for such a security system to indicate the current location of the monitored persons and objects, as well as to set off any one of a number of alarm conditions depending on the need for further investigation and assistance.
Automobile sales lots and congregate care facilities are characterized by an ever-changing inventory arrayed over a relatively large area which must be continually monitored for custodial purposes. Devices have been proposed to monitor unattended automobiles to prevent or discourage theft. Numerous different anti-theft devices have included various bars to lock onto an automobile steering wheel and which in some instances attach to the accelerator pedal.
Other efforts have employed hidden switches to disable the ignition system and shock and motion sensors. Such sensors, upon impulse, actuate an automobile disabling switch and alarm as shown in U.S. Pat. No. 4,990,890. Additionally, it has been proposed to equip vehicles with external radar to sense unauthorized tampering. These systems are relatively expensive and are sometimes ineffective to monitor a large number of vehicles or to make a record of the vehicle subjected to the unauthorized activity. Also, they fail to provide for automatic telecommunication of the alarm to either a central or remote area.
Vehicle security systems have been proposed which included a respective immobilizer and transceiver module in each vehicle. A number of security stations are provided to detect low power signals emitted by vehicles when an unauthorized act is detected. The signals are transmitted to a base station in response to a polling signal therefrom. The compromised vehicle may be immobilized by signals from either the base station or from a security station. A system of this type is disclosed in U.S. Pat. No. 4,990,890.
Other systems have been proposed which include a transmitter in each vehicle to broadcast an emergency signal unique to the vehicle indicative of the nature of the emergency condition. A central station includes a receiver responsive to the signal to operate a transmitter to transmit a disabling signal to a receiver in the vehicle. An alarm sensor can be mounted on each automobile to be monitored. When disturbed, the alarm sensor actuates an automatic dialer to send either a voice or a digital signal identifying the vehicle by a radio telephone to an alarm receiving station. Such systems are shown in U.S. Pat. Nos. 4,067,411 and 4,904,983. This system lacks a self contained transmission capability as it relies on the radio telephone.
Monitoring systems have been proposed which incorporate transmitters mounted on vehicles to be monitored and operative to transmit a watchdog periodic signal to a central receiving station. The transmitted signals become weak and disappear if the vehicles are removed from beyond a predetermined boundary area. The transmitters are responsive to unauthorized tampering to discontinue transmitting thereby generating an alarm. A system of this type is disclosed in U.S. Pat. No. 3,618,067
In congregate care facilities such as hospitals and nursing homes, monitoring is required so the custodian acting as an overseer can readily check the status of a patient's condition. Further, to be effective, a congregate caretaker must have the capability of quickly responding to any emergency call. In the past, patients have sometimes been provided with manually actuated devices such as pull cords or transmitter buttons to be used in case of emergency. These devices fail to communicate meaningful intelligence to enable the caretaker to determine whether the monitored item has moved from an authorized area or to discern the character of any distress call.
For persons moving about a large geographical area, such as students on a school campus, or security guards patrolling an industrial facility, monitoring systems have been proposed which call for the person to carry a portable tracking unit, such that a person or object may be located in an emergency by locating the tracking unit assigned to that student or guard. Several systems have been proposed that call for the tracking unit to be manually actuated to transmit a distress signal that includes a unique identification code for the particular tracking unit. The distress signal is received by a local receiver, which in turn relays the distress signal, along with a code identifying the particular receiver relaying the distress signal, to a monitoring center where an alarm is triggered and appropriate action may be taken. Such a system is shown in U.S. Pat. No. 5,365,217.
A system utilizing fixed transceivers mounted on street light poles, drawing the necessary electrical power from the local municipal power system that supplies power to the street lights, is shown in U.S. Pat. No. 4,998,095. A system that relies on a plurality of receivers to simultaneously receive the same distress signal so that the location of the tracking unit may be determined by comparing the strength of the distress signal at each receiver is shown in U.S. Pat. No. 5,115,224.
Another proposal, as shown in U.S. Pat. No. 5,572,195, calls for the tracking unit to comprise an infrared transmitter for transmitting an infrared identification code to a plurality of infrared receivers connected to a computer network and located within the area of interest. Finally, yet another proposal, this one calling for local receivers to include processors for processing the received distress signal before passing it on to a central processor which stores the distress signals for periodic determination of tracking unit location, is shown in U.S. Pat. No. 5,455,851.
The above described systems of the prior art, while providing various means for transmitting a distress signal to a central monitoring station, do not provide an adequate means to constantly track the location and motion of a mobile entity in the absence of a manually-actuated distress signal, nor do they provide an adequate alternative to the manual distress signal to detect an emergency situation when the mobile entity is not in a physical condition to manually actuate the distress signal, such as if a person is injured and incapacitated due to a fall. A security system is needed that provides for constant, real time tracking of mobile entities, while being further responsive to a number of alarm conditions to display alarms so assistance may be rendered.